1. Field of the Invention
The present invention relates to current monitors and more particularly to a current monitor for monitoring and accurately measuring current over a wide dynamic range.
2. Description of the Related Art
Many modern electronic devices draw current over a very wide range. A wide current range is especially inherent in devices designed to operate in a number of different modes, including standby and normal.
In the standby mode, a device usually draws only the necessary amount of current required to keep memory alive. Usually, the memory is established on an integrated circuit device and requires very little current to keep alive. In the normal operating mode, a device may draw current that is several orders of magnitudes higher than the standby mode current. In the normal operating mode, the current must be large enough to drive the internal components of the device, including associated electromechanical devices which can consume large amounts of current. In addition to driving the internal elements of the device, the normal operating mode current may be required to drive external components, for example, speakers in a stereo system. In many such devices, standby current may be as little as 0-50 mA, while normal operating current can go up to several amps.
A current monitor used to measure current through such devices must be capable of accurately measuring current over very wide dynamic ranges. However, conventional current monitors are not capable of accurately measuring current over such wide ranges.
Typical circuitry designed to measure low current levels (&lt;50 mA) would be damaged if high current were passed through it. Also, since larger shunt resistance values are used in low current sensors, the voltage drop developed across the shunt resistor at higher current levels may be large enough to adversely affect the voltage across the load being tested. Further, high current requires very high power resistors and large heat sinks which are not included in low current sensors. On the other hand, circuitry designed to measure high current levels are inappropriate for measuring low current because the larger range prevents the current sensor from being able to sufficiently discriminate between small current level differences.
Therefore, monitoring current over a wide range using conventionally available current monitors requires using either a number of separate current monitors, each having the appropriate current ranges wherein an operator connects and disconnects each monitor from the device as necessary, or a current monitor having several current ranges built in, wherein the operator manually switches between current ranges as necessary. Both solutions require the operator to monitor and respond to the measured current. These solutions are both cumbersome and impractical because the operator may be unable to continually monitor the actual current. Such a solution is also impractical because the current may change so rapidly that the operator is unable to react and shift the current range quickly enough to continuously monitor the current.